A typical power generator includes a shaft and a rotor carried by the shaft. Surrounding the generator rotor is a generator stator. A turbine, such as a gas combustion turbine, a water-driven turbine, or steam-driven turbine rotates the shaft. The generator rotor is supplied DC power typically from an exciter also driven by the shaft. As the generator rotor is turned within the generator stator, electrical power is produced and is delivered to the utility power grid.
The exciter typically includes an exciter rotor carried by a shaft connected to the generator shaft. An exciter stator surrounds exciter rotor. Regulated DC power is supplied to the exciter stator so that AC power is produced by the exciter rotor as the exciter rotor is rotated within the field produced by the exciter stator.
A rotating rectifier wheel, also called a diode wheel, is carried by the shaft of the exciter and converts the AC power from the exciter rotor into DC power that, in turn, is supplied to the generator rotor. A typical rectifying wheel includes a rotating base and a plurality of diodes carried by the base. A plurality of parallel connected diodes are typically provided for each phase of a multiphase exciter. A fuse is typically connected in series with each diode so that if the diode short-circuits, the fuse can isolate the defective diode. When sufficient redundancy is provided in the form of multiple diodes and fuses for each phase, one or more diodes or fuses may fail and the rectifier can still be operated. The exciter can be taken out of service and the defective components repaired at a more convenient time.
A typical approach to determining whether any of the fuses has blown is to visually inspect the rotating rectifying wheel while it is in service by using a stroboscope aimed into the exciter housing. A typical fuse may include a pop-out indicator that extends outwardly from the fuse housing when the fuse has failed. An example of such a fuse is disclosed in U.S. Pat. No. 6,256,183 B1 to Mosesian. Unfortunately, this approach requires careful visual inspection on a regular basis.
A similar approach to determine a fuse failure while the rectifying wheel is in service is disclosed in U.S. Pat. No. 3,030,551 to Lessman. This patent discloses a light connected to glow when the corresponding fuse has blown. Unfortunately, this approach also requires visual inspection using a stroboscope. Similarly, U.S. Pat. No. 3,866,196 to Mann et al. discloses a blown fuse indicator including a projectile that is normally held against movement and is released when the fuse blows. It can then be observed using a stroboscope as described above.
U.S. Pat. No. 4,164,705 to Whitney et al. discloses sensing current in the salient poles of the exciter stator. Variations in the sensed current can indicate a number of abnormal conditions, such as whether a fuse has blown.
U.S. Pat. No. 4,349,813 to Ishibashi et al. discloses a current transformer coupled between the fuse and diode. Voltage pulses induced by the secondary winding are received by a pulse extinction detection circuit. When the pulses are not detected, the pulse extinction detection circuit produces a DC signal. Along these lines, U.S. Pat. No. 4,635,044 to South discloses an apparatus for remote sensing of a failed fuse by sensing a current flow through each fuse. The operation of the current sensors is coordinated to the rotation of the wheel by an angle position oscillator that produces a constant stream of pulses at a preselected rate. Further, U.S. Pat. No. 6,466,032 B2 to Klaar discloses sensing electromagnetic pulses produced during the disconnection of the fuse by receiving the pulses at a station antenna. An encoder is also provided to determine the angular position of the rotating wheel.
U.S. Pat. No. 4,952,915 to Jenkins et al. discloses light emitting diode detectors carried by the rotating wheel being grouped to display concentric circles of light while operating. Stationary sensors are also provided to sense the LEDs, and the LEDs are connected so that if a fuse fails, the LED is lit. No synchronization is required between the detection circuit and the rotation of the rectifier wheel to thereby simplify construction and operation.
Despite continuing efforts to determine when a fuse of a rectifying wheel is blown, there still exists a need for a more reliable and effective system and method.